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Putting in the ground work

Spotlight - Extensive piling is giving a burnt-out warehouse a new lease of life.

Conversion of a former bonded warehouse into luxury quayside apartments in Newcastle-upon-Tyne and a new development on an adjacent plot are both making use of a host of specialist foundation systems.

The seven-storey Grade II listed warehouse was ravaged by fire two years ago, leaving little structural support.

But a new steel frame erected within the shell of the old warehouse will give the structure new strength.

Piling and foundations contractor Roger Bullivant is installing 264 mini piles to bear the load of the new structure and flight augered piled foundations and a series of ground anchors for the new build development.

The warehouse will offer 48 apartments and the new-build block will house 86 flats.

Developing a pair of apartment blocks on the site of a dilapidated warehouse is proving a considerable challenge, according to property developer Mandale's senior site manager Peter Remmington.

'This is certainly one of the most complex jobs I have ever worked on, ' he says. 'The steel framework we are building within the old warehouse has to tie in to and secure the remaining brick and stone facade. The walls had buckled in the fire and it was too risky to put loadings on the old structure.

'Development of the second (new) apartment block is also tricky because the site needs to be reduced in height and is bordered by a road that cannot be moved, ' he adds.

The fire-damaged warehouse façade was being supported solely by charred timber beams, so a large scaffold tower was erected on one side of the warehouse to provide some temporary support.

A new concrete oor had to be founded on piles at the base of the building to support the steel frame, but a rig with a large mast could not be used because of restricted headroom beneath the timber beams. A top driven mini rig was chosen to install 183 steel tubular piles on the ground floor to pick up point loads from the steel frame. The 140mm diameter piles extended 8m into the ground.

Once the tubular piles were in place, 82 drilled and cased 220mm diameter mini piles were formed on top of the historic city wall, built in 1311, to support the internal steel frame above ground level, along one side of the warehouse.

A row of 126 sectional ight augered (SFA) piles has been installed to depths of between 10m and 16m to form a contiguous piled retaining wall running beside the new apartment building.

The wall is being built to support Hanover Street, a cobbled highway that runs along the rear of the site. The ground in front of the road could then be lowered, reducing the overall height of the building.

Creating an SFA pile involves connecting together a series of 2m long sections of auger as the ight descends into the ground.

At full depth, concrete is pumped through a central shaft and the rotation of the auger is reversed to form a column of concrete. A cage of eight reinforcing bars is then lowered by crane and pushed into each concrete pile to full depth to provide added strength.

The ground level in front of the wall was dropped by 5m in May, allowing work on the 80, 10.5m hollow stem anchors to be installed.

These were then placed between the vertical piles at 700mm intervals to support the wall during the construction phase. Each anchor is drilled into the ground at between 20° and 30° using a sacricial ballistic bit attached to a threaded steel bar.

Each ballistic bit is formed from tungsten carbide and is drilled into the embankment using a piling rig that delivers a 'drifting load' of repeated hammering action, aided by a flush of water. Once the anchor has reached full depth, two operatives insert a pair of 10m long threaded steel bars to give each anchor added strength.

Once the anchors are in place the ground level will be dropped by another 5m to form a level platform for the second apartment block.

Conversion of the old bonded warehouse and construction of the new apartment block are set to be nished by November.

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